Polymer particle coated with silica, method for producing the same and use of the same

ABSTRACT

A polymer particle coated with silica comprising: a polymer particle derived from a polymerizable vinyl-based monomer; and a silica film covering the polymer particle, which makes a surface of the polymer particle expose so that an aperture ratio of 0.1 to 1 is possessed and a height h of the silica film and a diameter D of the polymer particle coated with silica have a relationship of 0.5≦h/D&lt;1, wherein the silica film includes a polyalkoxysiloxane oligomer condensate.

This application is a 371 of PCT/JP04/04061 filed Mar. 24, 2004.

TECHNICAL FIELD

This invention relates to a polymer particle coated with silica, amethod for producing the same, and use of the same. More specifically,this invention relates to a polymer particle coated with silica havingexcellent light diffusibility/reflectivity, a method for producing thesame, and use of the same. The polymer particle coated with silica ofthis invention can be particularly useful for a coating composition, acoated article, an optical member, a liquid crystal display and a lightdiffusible molded article.

BACKGROUND ART

Conventionally, as a coating composition including a composition for apaint material, a composition with particles blended therein has beenused in order to attain various objects utilizing light diffusibilitypossessed by the particles. For example, for the purpose of mattingsurfaces of various molded articles, there has been used a coatingcomposition in which inorganic particles such as silica particles ororganic polymer particles (resin particles) are blended. Since a coatedfilm obtained from the above coating composition has a surface on whichirregularities are formed and reflection of light is diffused, a surfaceis matted.

In addition, in an image display device used in a TV set, a personalcomputer, an electronic notebook, a cellular phone, an amusementapparatus and the like, an optical sheet for diffusing transmitted lightor reflected light is used as a light diffusing sheet or an antiglaresheet. Also in this optical sheet, in order to diffuse the transmittedlight or the reflected light, a coated film is formed on a surfacethereof. As a coating composition for forming the coated film on thesurface, there has been used a composition in which inorganic particlesor resin particles are blended.

For example, in the light diffusing sheet for diffusing the transmittedlight, as a coating composition, there has been used a composition withparticles of inorganic substances such as calcium carbonate and silica,or organic polymers such as polystyrene and silicone blended therein.

However, the inorganic particles have a problem of low dispersionstability in a binder solution, in particular, a binder solution using atransparent binder such as a polymethyl methacrylate resin as a binderresin.

In addition, in a coating composition with organic polymer particlesblended therein, dispersion stability is better, but there is a problemthat sufficient light diffusibility is not obtained.

On the other hand, in optical components such as an illuminationapparatus cover, a lens, a light guiding plate, a video disc, a screenfor a projection television, and various molded articles such as acosmetic container, a front plate of a vending machine, a signboard, amerchandise display and a table container, in order to enhance amerchandise value such as their aesthetic property, improvement of lightdiffusibility has been challenged by molding the above articles using araw material in which light diffusible particles are blended in a resin.In these molded articles, various resins, in particular, thermoplasticresins such as a polycarbonate resin, a polystyrene resin and apolyacrylate resin are used as a base material.

Conventionally, as the light diffusible particle used in the moldedarticles, there have been well-known inorganic particles such as glass,calcium carbonate and silica, or resin particles such as a polyacrylateresin and a polystyrene resin.

However, these molded articles have a problem that transparency isdegraded due to blend of the light diffusible particles and, also,improvement in light diffusibility is not sufficient.

In response to these problems, Japanese Patent No. 3,040,705 proposes apolymer particle containing smectite, and Japanese Unexamined PatentPublication No. Hei 10(1998)-265580 proposes a composite particle inwhich silica particles of 500 nm or less are dispersed in resinparticles.

However, even a composition using one of the above particles asparticles to be blended can not still provide a coated article or amolded article having sufficient light diffusibility.

Additionally, in addition to those described in the above publications,a composite particle in which a surface of a polymer particle is coveredwith other polymer or an inorganic material has been also known.

Among these, the latter composite particle in which the surface of thepolymer particle is covered with the inorganic material has an advantagethat a refractive index at an interface between the polymer particle andthe inorganic material is made greater than a refractive index at aninterface between the polymers of the former.

A composite particle in which a surface of polymer particle is coveredwith an inorganic material has been reported, for example, in JapaneseUnexamined Patent Publication No. Hei 5(1993)-170924. This publicationdescribes a composite particle in which a substance smaller than aparticle of a thermoplastic substance and excellent in heat resistanceis immobilized on the particle of a thermoplastic substance. Thecomposite particle is obtained by a mechanical shear force by raising atemperature of the particle of the thermoplastic substance to asoftening temperature or more, and stirring a substance excellent inheat resistance and the particle of the thermoplastic substance.

The composite particle obtained by the method of Japanese UnexaminedPatent Publication No. Hei 5(1993)-170924 has a structure that thesurface of the particle of the thermoplastic substance is approximatelyuniformly covered with the substance excellent in heat resistance, hasslightly improved in light diffusibility and reflectivity rather thanthe particle of the thermoplastic substance as a raw material; however,further improvement is demanded.

In addition, in the above method, since a mechanical shear force isapplied to the particle of the thermoplastic substance, it is requiredthat the particles of the thermoplastic substance endure this shearforce, and there is a problem that a usable substance is limited.

Furthermore, it is required that the particle of the thermoplasticsubstance is prepared in advance before subjected to the method, andfurther omission of a step is desired from a viewpoint of saving of amanufacturing cost.

DISCLOSURE OF THE INVENTION

In order to solve the aforementioned problems, the present inventorintensively studied and, as a result, have unexpectedly found that, byaqueous suspension-polymerizing a polymerizable vinyl-based monomer inthe presence of a polyalkoxysiloxane oligomer having nocopolymerizability with the polymerizable vinyl-based monomer and, then,condensing with the polyalkoxysiloxane oligomer, a silica film derivedfrom the polyalkoxysiloxane oligomer can be formed so that a surface ofa polymer particle is exposed, and the resulting polymer particle coatedwith silica is excellent in light diffusibility and reflectivity, whichresulted in completion of this invention.

In addition, the present inventors have also found that the polymerparticle coated with silica can impart excellent light diffusibility andreflectivity to a coated article or a molded article by blending in acoating composition or a molded article.

Thus, according to this invention, there is provided a polymer particlecoated with silica comprising: a polymer particle derived from apolymerizable vinyl-based monomer; and a silica film covering thepolymer particle, which makes a surface of the polymer particle exposeso that an aperture ratio of 0.1 to 1 is possessed and a height h of thesilica film and a diameter D of the polymer particle coated with silicahave a relationship of 0.5≦h/D<1, wherein the silica film includes apolyalkoxysiloxane oligomer condensate.

According to this invention, there is also provided a coatingcomposition comprising: a polymer particle coated with silica comprisinga polymer particle derived from a polymerizable vinyl-based monomer, anda silica film covering the polymer particle, which makes a surface ofthe polymer particle expose so that an aperture ratio of 0.1 to 1 ispossessed and a height h of the silica film and a diameter D of thepolymer particle coated with silica have a relationship of 0.5≦h/D<1,the silica film including a polyalkoxysiloxane oligomer condensate; anda binder solution, wherein the binder solution contains a binder resinand a solvent.

In addition, according to this invention, there are also provided acoated article in which the aforementioned coating composition is coatedon a substrate, an optical member in which the aforementioned coatingcomposition is coated on a transparent substrate, and a liquid crystaldisplay in which the optical member is used.

Furthermore, according to this invention, there is also provided a lightdiffusible molded article comprising a transparent resin and a polymerparticle coated with silica, wherein the polymer particle coated withsilica comprises a polymer particle derived from a polymerizablevinyl-based monomer, and a silica film covering the polymer particle,which makes a surface of the polymer particle expose so that an apertureratio of 0.1 to 1 is possessed and a height h of the silica film and adiameter D of the polymer particle coated with silica have arelationship of 0.5≦h/D<1, and the silica film includes apolyalkoxysiloxane oligomer condensate.

Still further, according to this invention, there is also provided amethod for producing a polymer particle coated with a silica film whichmakes a surface of the polymer particle expose so that an aperture ratioof 0.1 to 1 is possessed, and a height h of the silica film and adiameter D of the polymer particle coated with silica have arelationship of 0.5≦h/D<1, the method comprising, in the followingorder, the steps of: uniformly mixing 100 parts by weight of apolymerizable vinyl-based monomer, 10 to 500 parts by weight of apolyalkoxysiloxane oligomer which is inert to the polymerizablevinyl-based monomer, and 0.01 to 10 parts by weight of a polymerizationinitiator to obtain a monomer composition; aqueoussuspension-polymerizing the polymerizable vinyl-based monomer in themonomer composition in the presence of a suspension stabilizer to obtaina polymer particle; and adding an acid or base catalyst to condense thepolyalkoxysiloxane oligomer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a polymer particle coatedwith silica of this invention.

FIG. 2 is a schematic cross-sectional view of a silica particle obtainedby firing the polymer particle coated with silica of this invention.

FIG. 3 is a conceptual view for illustrating a method of measuring anaperture ratio in this invention.

FIG. 4 is a schematic cross-sectional view showing a sheet-like lightdiffusible molded article containing the polymer particle coated withsilica.

BEST MODE FOR CARRYING OUT THE INVENTION

The polymer particle coated with silica of this invention has astructure having anisotropy in which a surface of a spherical orapproximately spherical polymer particle 1 is coated (covered) with asilica film 2 so that an aperture ratio is 0.1 to 1, as shown in across-sectional view of FIG. 1. In the figure, a reference number 3means a polymer particle coated with silica. By having such thestructure, as compared with a particle having no anisotropy such as aspherical silica particle, and a composite particle in which a surfaceof a polymer particle is completely coated with a silica film,complicated light reflection and refraction occur and, as a result,strong light diffusibility and reflectivity can be exhibited. When theaperture ratio of the silica film is less than 0.1, light diffusibilityand reflectivity become poor and, when the aperture ratio exceeds 1,peeling of the film easily occurs, being not preferable. The apertureratio is more preferably 0.1 to 0.8. The polymer particle coated withsilica having an aperture ratio of 1 means that the silica film coversapproximately a half of the particle.

A method of measuring an aperture ratio will be described in EXAMPLES tobe described later. Herein, as an aperture ratio, the polymer particlecoated with silica is fired to burn out the polymer particle to obtain asilica particle, and an aperture ratio of the silica particle is used.The aperture ratio of the silica particle has a value strictly differentfrom the aperture ratio of the silica film in some cases, by shrinkageof the silica film at firing, or by lack of a thin region at an end of asilica covering, but the present inventor confirmed that the apertureratio of the silica film of the polymer particle coated with silica isapproximately consistent with the aperture ratio of the silica particle.

A height h of the silica film and a diameter D of the polymer particlecoated with silica have a relationship of 0.5≦h/D<1. When h/D is 1,light diffusibility and reflectivity become poor, being not preferable.When h/D is less than 0.5, peeling of the film easily occurs, being notpreferable.

A method of measuring h/D will be described in EXAMPLES. Herein, as h/D,the polymer particle coated with silica is fired to burn out the polymerparticle to obtain the silica particle, and h/D of the silica particleis used. And, the h/D of the silica particle has a value strictlydifferent from the h/D of the polymer particle coated with silica insome cases, by shrinkage of the silica film at firing, or by lack of thethin region at an end of the silica covering. However, the presentinventors confirmed that the h/D of the polymer particle coated withsilica is approximately consistent with the h/D of the silica particle.

The polymer particle coated with silica of this invention will bedescribed below by referencing a method for producing the same.

First, the polymerizable vinyl-based monomer which can be used in thisinvention is not particularly limited. Examples thereof include styreneand a derivative thereof such as styrene, o-methylstyrene,m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene,p-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene,p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene,p-n-dodecylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene,and 3,4-dichlorostyrene, vinyl esters such as vinyl acetate, vinylpropionate, and vinyl butyrate, α-methylene aliphatic monocarboxylicacid esters such as methyl acrylate, ethyl acrylate, propyl acrylate,n-butyl acrylate, isobutyl acrylate, n-octyl acrylate, dodecyl acrylate,2-ethylhexyl acrylate, stearyl acrylate, lauryl acrylate, 2-chloroethylacrylate, phenyl acrylate, methyl α-chloroacrylate, methyl methacrylate,ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutylmethacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexylmethacrylate, stearyl methacrylate, lauryl methacrylate, phenylmethacrylate, dimethylaminoethyl acrylate, dimethylaminoethylmethacrylate, diethylaminoethyl acrylate, and diethylaminoethylmethacrylate, and acrylic acid and methacrylic acid derivatives such asacrylonitrile, methacrylonitrile, acrylamide, methacrylamide,2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethylmethacrylate, and 2-hydroxypropyl methacrylate. Optionally, acrylicacid, methacrylic acid, maleic acid, and fumaric acid may be used.Furthermore, these may be used by combining two or more.

In addition, vinyl ethers such as vinyl methyl ether, vinyl ethyl ether,and vinyl isobutyl ether, vinyl ketones such as vinyl methyl ketone,vinyl hexyl ketone, and methyl isopropenyl ketone, N-vinyl compoundssuch as N-vinylpyrrole, N-vinylcarbazole, N-vinylindole, andN-vinylpyrrolidone, and vinyl naphthalene salt may be used alone or incombination of two or more in such a range that an effect of thisinvention is not prevented.

Among these, styrene and methyl methacrylate and the like which areinexpensive in a cost are preferable.

In addition, the polymer particle may be crosslinked with a monomerhaving two or more functional groups such as ethylene glycoldimethacrylate, polyethylene glycol dimethacrylate, and divinylbenzene.

In particular, when the polymer particle coated with silica is used in asystem containing an organic solvent, it is preferable that the polymerparticle is crosslinked. The amount of a preferable crosslinking agent(the aforementioned monomer having two or more function groups) to beadded is preferably 1 to 50 parts by weight, particularly preferably 3to 40 parts by weight, per 100 parts by weight of the polymerizablevinyl-based monomer (monomer having one functional group). When theaddition amount is less than 1 part by weight, the resulting polymerparticle is dissolved or swollen in the organic solvent in some cases,being not preferable.

In this invention, a polyalkoxysiloxane oligomer which is a precursor ofthe silica film is inert (means that it is not copolymerized) to thepolymerizable vinyl-based monomer, and the oligomer having the followingstructural formula can be used.

Among the aforementioned structural formula, examples include oligomersof polymethoxysiloxane, polyethoxysiloxane, polypropoxysiloxane, andpolybutoxysiloxane. Among these, the polymethoxysiloxane oligomer, andthe polybutoxysiloxane oligomer which are hardly water-soluble and arebetter in phase separation with a resin are preferable. Particularlypreferable are the polymethoxysiloxane oligomer and thepolybutoxysiloxane oligomer having a weight-average molecular weight of300 to 3000, more preferably 300 to 2000. When the weight-averagemolecular weight is less than 300, or exceeds 3000, it becomes difficultto form the silica film in both, cases, being not preferable.

The weight-average molecular weight is measured using GPC under thefollowing conditions:

Column: “TSK GEL” (made by Tosoh Corp.)

-   -   G-1000H    -   G-2000H    -   G-4000H

Eluent: tetrahydrofuran

Eluting rate: 1 ml/min

Eluting temperature: 40° C.

In low-molecular alkoxysiloxane in which n is 1 to 2 in theaforementioned molecular formula, such as tetramethoxysilane andtetraethoxysilane, since water-solubility becomes strong by hydrolysisof a functional group, it becomes difficult to be stably present in amonomer droplet, being not preferable. In addition, thepolyalkoxysiloxane oligomer in which n is 40 or more in theaforementioned molecular formula is not preferable because compatibilitywith the polymerizable vinyl-based monomer or condensability of itselfis reduced.

The amount of the polyalkoxysiloxane oligomer to be added is preferably10 to 500 parts by weight, further preferably 20 to 300 parts by weight,per 100 parts by weight of the polymerizable vinyl-based monomer. Whenthe amount is less than 10 parts by weight, it is difficult to realizethe covering state in this invention, being not preferable. When theamount is more than 500 parts by weight, it is not preferable that thestate of exposure of the polymer particle is realized with difficulty.

In addition, for the purpose of imparting function of ultraviolet-rayabsorption to these polyalkoxysiloxane oligomers, a hydrolysable alkoxymetal compound other than a silicon series may be added.

For polymerizing the polymerizable vinyl-based monomer, a polymerizationinitiator is used. Examples of the polymerization initiator includeoil-soluble peroxide series polymerization initiator and azo seriesinitiator which are usually used in aqueous suspension polymerization.Specific examples include peroxide series polymerization initiators suchas benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, benzoylorthochloroperoxide, benzoyl orthomethoxyperoxide, methyl ethyl ketoneperoxide, diisopropyl peroxydicarbonate, cumene hydroperoxide,cyclohexanone peroxide, t-butyl hydroperoxide, and diisopropylbenzenehydroperoxide, and azo series initiators such as2,2′-azobisisobutyronitrile,

-   2,2′-azobis(2,4-dimethylvaleronitrile),-   2,2′-azobis(2,3-dimethylbutyronitrile),    2,2′-azobis(2-methylbutyronitrile),-   2,2′-azobis(2,3,3-trimethylbutyronitrile),-   2,2′-azobis(2-isopropylbutyronitrile),-   1,1′-azobis(cyclohexan-1-carbonitrile),-   2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile,-   (2-carbamoylazo)isobutyronitrile, 4,4′-azobis(4-cyanovaleric acid),    and-   dimethyl-2,2′-azobisisobutyrate.

Among these, 2,2′-azobisisobutyronitrile,2,2′-azobis(2,4-dimethylvaleronitrile), benzoyl peroxide, lauroylperoxide and the like are preferable in terms of a degradation rate ofthe polymerization initiator. The polymerization initiator is used atpreferably, 0.01 to 10 parts by weight, more preferably 0.1 to 5.0 partsby weight, per 100 parts by weight of the polymerizable vinyl-basedmonomer. When the polymerization initiator is less than 0.15 parts byweight, it is difficult to exert function of polymerization initiation.On the other hand, when the polymerization initiator is used at anamount exceeding 10 parts by weight, this is not economical from aviewpoint of a cost.

In order to color the silica film, a metal oxide pigment such astitanium oxide, zinc oxide, magnesium oxide, chromium oxide, andzirconium oxide may be used. However, an organic pigment, a metalhydroxide pigment, a dye and the like are not preferable since astructure thereof is changed at sintering or burning.

The polymerizable vinyl-based monomer, the polyalkoxysiloxane oligomer,the polymerization initiator and other component are uniformly mixed bythe well-known method to obtain a monomer composition.

Then, examples of an aqueous medium for aqueous suspension-polymerizingthe monomer composition include water, a mixed medium of water and awater-soluble solvent such as an alcohol. The amount of the aqueousmedium to be used is usually 100 to 1000 parts by weight per a total 100parts by weight of the polymerizable vinyl-based monomer and thepolyalkoxysiloxane oligomer in order to stabilize a suspensionpolymerization particle.

In addition, in order to suppress generation of an emulsified particlein an aqueous system, a water-soluble polymerization inhibitor such asnitrites, sulfites, hydroquinones, ascorbic acids, water-soluble vitaminBs, citric acid, and polyphenols may be used.

Furthermore, if necessary, a suspension stabilizer may be added to theaqueous medium. Examples thereof include phosphate such as calciumphosphate, magnesium phosphate, aluminum phosphate, and zinc phosphate,pyrophosphate such as calcium pyrophosphate, magnesium pyrophosphate,aluminum pyrophosphate, and zinc pyrophosphate, and a dispersionstabilizer of a hardly water-soluble inorganic compound such as calciumcarbonate, magnesium carbonate, calcium hydroxide, magnesium hydroxide,aluminum hydroxide, calcium metasilicate, calcium sulfate, bariumsulfate, and colloidal silica. Among these, tri calcium phosphate,magnesium pyrophosphate and calcium pyrophosphate obtained by a doubledecomposition production method, and colloidal silica are preferablesince the polymer particle can be stably obtained.

In addition, it is also possible to use a surfactant such as anionicsurfactant, cationic surfactant, amphoteric surfactant, and nonionicsurfactant together with the aforementioned suspension stabilizer.

Examples of the anionic surfactant include a fatty acid oil such assodium oleate, and potassium castor oil, an alkyl sulfate ester saltsuch as sodium laurylsulfate, and ammonium laurylsulfate, analkylbenzene sulfonate salt such as sodium dodecylbenzenesulfonate, analkylnaphthalenesulfonate salt, an alkanesulfonate salt, adialkylsulfosuccinate salt, an alkyl phosphate ester salt, anaphthalenesulfonic acid formalin condensate, and a polyoxyethylenealkyl phenyl ether sulfate ester salt, a polyoxyethylene alkylsulfateester salt and the like.

Examples of the nonionic surfactant include polyoxyethylene alkyl ether,polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester,sorbitan fatty acid ester, polyoxysorbitan fatty acid ester,polyoxyethylene alkylamine, glycerin fatty acid ester,oxyethylene-oxypropylene blocked polymer and the like.

Examples of the cationic surfactant include alkylamine salt such aslaurylamine acetate, and stearylamine acetate, and quaternary ammoniumsalt such as lauryltrimethylammonium chloride, and the like.

Examples of the amphoteric surfactant include lauryldimethylamine oxide,and phosphate ester series or phosphite ester series surfactant, and thelike.

These suspension stabilizers and surfactants may be used alone, or incombination of two or more, and they are used by appropriately adjustingselection and the use amount of the suspension stabilizer in view of aparticle diameter of the resulting polymer particle and dispersionstability at polymerization. Usually, the amount of the suspensionstabilizer to be used is 0.5 to 15 parts by weight per 100 parts byweight of the polymerizable vinyl-based monomer, and the amount of thesurfactant to be added is 0.001 to 0.1 parts by weight per 100 parts byweight of the aqueous medium.

The monomer composition is added to the thus adjusted aqueous medium,and aqueous suspension polymerization is performed.

Examples of a method of dispersing the monomer composition include amethod of directly adding the monomer composition to the aqueous medium,and dispersing as a monomer droplet in the aqueous medium by a stirringforce of a propeller, and a method of dispersing using a homomixer whichis a dispersing machine configured by a rotor and a stator utilizing ahigh shear force, or an ultrasound dispersing machine, and the like.Among these, when the monomer composition is dispersed with a highpressure-type dispersing machine utilizing collision between monomerdroplets or an impact force against a machine wall, such as amicrofluidizer, and a nanomizer, or by a method of pressing a monomercomposition into an aqueous medium through a MPG (Micro Porous Glass)porous membrane, it is preferable that a particle diameter is moreuniformized.

Then, by heating the aqueous medium in which a monomer composition as aspherical monomer droplet is dispersed, suspension polymerization isinitiated. During a polymerization reaction, it is preferable to stirthe aqueous medium, and stirring may be mildly performed to such anextent that floating of a monomer droplet or settlement of particlesafter polymerization can be prevented.

In suspension polymerization, the polymerization temperature ispreferably about 30 to 100° C., more preferably about 40 to 80° C. Thetime during which this polymerization temperature is retained ispreferably about 0.1 to 20 hours.

When the boiling point of the polymerizable vinyl-based monomer or thepolyalkoxysiloxane oligomer is around a polymerization temperature ornot lower than a polymerization temperature, it is preferable thatpolymerization is performed under sealing or under pressure by using apressure resistant polymerization facility such as an autoclave so thatthe polymerizable vinyl-based monomer and the polyalkoxysiloxaneoligomer are not volatilized.

Then, by condensing the polyalkoxysiloxane oligomer, the polymerparticle coated with silica of this invention can be obtained. Examplesof the method of condensing the polyalkoxysiloxane oligomer includedehydration condensation using an acid catalyst or a base catalyst. Asthe acid catalyst and the base catalyst, hydrochloric acid, sulfuricacid, nitric acid, ammonia, sodium hydroxide, potassium hydroxide, andammonium nitrate can be used. When a manufacturing container is made ofa steel or a stainless steel, sodium hydroxide and ammonia which arebasic are preferable from a viewpoint of corrosion. The amount of thecatalyst to be added is preferably 0.01 to 30 parts by weight, morepreferably 1 to 15 parts by weight, per 100 parts by weight of thepolyalkoxysiloxane oligomer.

After condensation, if necessary, the suspension stabilizer is degradedwith hydrochloric acid, the polymer particle coated with silica isseparated as a hydrous cake by a method such as suction filtration,centrifugation dehydration, centrifugation, pressure dehydration and,further, the resulting hydrous cake is washed with water, and dried,thereby, an objective polymer particle coated with silica can beobtained.

As described above, since the method of this invention is not a methodof applying a high shear force to cover the polymer particle with thesilica particle, even low heat resistant polymer particle having Tg(glass transition point) of less than 80° C. can be easily coated.Examples of a polymer having Tg of lower than 80° C. include polyethylacrylate, poly n-butyl acrylate, polyisobutyl acrylate, polylaurylacrylate, polystearyl acrylate, poly 2-ethylhexyl acrylate, polyethylmethacrylate, poly n-butyl methacrylate, polyisobutyl methacrylate,polylauryl methacrylate, polystearyl methacrylate, poly 2-ethylhexylmethacrylate and the like.

A size and a shape of the polymer particle coated with silica of thisinvention are not particularly limited. According to the aforementionedmethod for producing the polymer particle coated with silica, theparticle having the volume-average particle diameter of 1 to 100 μm canbe obtained.

Herein, adjustment of the volume-average particle diameter of theparticle can be performed by adjusting condition for mixing the monomercomposition and water, the addition amount of the suspension stabilizeror the surfactant, stirring condition for the stirrer, or dispersingcondition.

The polymer particle coated with silica, composite particle, of thisinvention contains a silica film at preferably 10 to 500 parts byweight, more preferably 20 to 300 parts by weight, per 100 parts byweight of the polymer particle.

According to this invention, the polymer particle coated with silicahaving a specular reflectance (definition is described in EXAMPLES) of 3to 13% can be provided. This value is a value lower than about 14% whenthe polymer particle is completely coated with the silica film,indicating that the polymer particle coated with silica of thisinvention is excellent in light diffusibility and reflectivity. When aspecular reflectance is 5 to 13%, light diffusibility and reflectivityare particularly excellent.

In addition, a coating composition of this invention has a compositionin that the aforementioned polymer particle coated with silica isblended in a binder solution containing a binder resin and a solvent.Since the coating composition of this invention is characterized in thatthe silica-film is provided so that a surface of the polymer particle isexposed although its action is not clear, compatibility between, anddispersion stability of the polymer particle coated with silica and thebinder resin are excellent. In addition, in the polymer particle coatedwith silica, complicated light reflection and refraction occur and, as aresult, it is thought that more excellent light diffusibility isexhibited.

Furthermore, a coated article is excellent in dispersion stability ofthe particle and, moreover, excellent in light diffusibility can beobtained using the coating composition of this invention.

The polymer particle coated with silica used in the coating compositionhas a volume-average particle diameter of usually 1 to 100 μm,preferably 3 to 50 μm, further preferably 3 to 30 μm. A method ofmeasuring the volume-average particle diameter is described in EXAMPLES.

When the volume-average particle diameter of the polymer particle coatedwith silica is less than 1 μm, there is a possibility that sufficientlight reflectivity is not obtained, being not preferable. When thediameter exceeds 100 μm, there is a possibility that appearance of acoated article is deteriorated, being not preferable.

As the binder resin constituting the binder solution, usually, athermoplastic resin is used, and examples of the thermoplastic resininclude (meth)acrylic resin, alkyl (meth)acrylate-styrene copolymerresin, polycarbonate resin, polyester resin, polyethylene resin,polypropylene resin, polystyrene resin, silicone resin, urethane resin,epoxy resin, melamine resin, vinyl acetate resin, phenol resin, resorcinresin, butadiene acrylonitrile rubber and the like.

Among these, when excellent transparency is required in a member aftercoating, such as the coating composition for an optical member,(meth)acrylic resin, alkyl (meth)acrylate-styrene copolymer resin,polycarbonate resin, and polyester resin are preferable. Thesethermoplastic resins can be used alone, or in a combination of two ormore.

The solvent constituting the binder solution is not particularly limitedas far as solubility or dispersibility of the binder resin is notproblematic, and examples include one or two or more kinds ofhydrocarbon solvents such as n-butane, n-hexane, n-heptane, n-octane,isononane, n-decane, n-dodecane, cyclopentane, cyclohexane, andcyclobutane, ketone solvents such as acetone, methyl ethyl ketone,methyl isobutyl ketone, cyclohexanone, and isophorone, ester solventssuch as ethyl acetate, and butyl acetate, ether alcohol solvents such asethylene glycol monomethyl ether acetate, ethylene glycol monoethylether, ethylene glycol monobutyl ether, and diethylene glycol monoethylether, alcohol solvents such as ethanol, isopropanol, n-butanol, andisobutanol, aromatic solvents such as toluene, xylene, and catechol,water and the like.

In an aqueous binder solution using the solvent of water or an alcoholseries, it is not necessary that the binder resin is not completelydissolved in the solvent, but may be dispersed in a form of an emulsionor a dispersion.

Among the aforementioned exemplification, examples of the particularlypreferably solvent include methyl ethyl ketone, cyclohexanone, ethylacetate, butyl acetate, and toluene in view of solubility of the binderresin, and a drying rate after coating. In addition, as the aqueousemulsion or dispersion, an emulsion or a dispersion of an acryl seriesor a polyester series is easily available, and transparency of a resinis high, being preferable.

In the coating composition of this invention, the amount of the polymerparticle coated with silica to be blended is usually 1 to 150 parts byweight, preferably 1 to 120 parts by weight, per 100 parts by weight ofa binder resin.

When the amount is 1 part by weight or more, more sufficient lightdiffusibility and light reflectivity are obtained. When the amount is150 parts by weight or less, there is no possibility that dispersionstability of the composite particle and adherablity to the adhered suchas a substrate are reduced.

In the case of a diffusion sheet for diffusing transmitted lightcomposed of a transparent substrate and a coated article, the amount ofthe polymer particle coated with silica in the coating composition to,be blended is preferably 20 to 120 parts by weight, more preferably 20to 100 parts by weight, per 100 parts by weight of the binder resin. Inthe case of an antiglare sheet for diffusing reflected light, the amountis preferably 1 to 30 parts by weight, more preferably 5 to 30 parts byweight.

In addition, the amount of the solvent to be blended is not particularlylimited as far as it is such the amount that the binder resin can besufficiently uniformly dissolved or dispersed and the silica-coatedpolymer particle can be sufficiently uniformly dispersed, but ispreferably 100 to 1000 parts by weight per 100 parts by weight of thebinder resin. When the amount is less than 100 parts by weight, there isa possibility that the binder resin is not sufficiently uniformlydissolved or dispersed, being not preferable. When the amount exceeds1000 parts by weight, since a viscosity of the coating composition isremarkably decreased, it is not preferable to becomes difficult toprepare a uniform coated article (coated film).

In the coating composition in this invention, in order to impartfunction of duster, opaqueness, or color to a coated article, inorganicpigments such as titanium oxide, zinc oxide, zirconium oxide, magnesiumoxide, iron oxide, iron hydroxide, chromium oxide, chromium hydroxide,ultramarine, Prussion blue, manganese violet, ultramarine purple,titanium black, carbon black, aluminum powder, mica titanium, bismuthoxychloride, iron oxide-treated mica titanium, Prussion blue-treatedmica titanium, carmine-treated mica titanium, silica, calcium carbonate,magnesium carbonate, barium sulfate, barium silicate, calcium silicate,magnesium silicate, calcium phosphate, hydroxyapatite, zeolite, alumina,talc, mica, bentonite, kaolin, and sericite, or organic pigments such asaluminum lake such as Tartrazine, Sunset Yellow FCF, brilliant blue FCF,zirconium lake, barium lake, Helindone Pink CN, Lithol Rubine BCA, lakered CBA, phthalocyanine blue, and permanent orange may be blended.

The amount of the pigment to be blended is preferably 1 to 80 parts byweight per 100 parts by weight of the binder resin. When the amount isless than 1 part by weight, an effect of the pigment such as coloring isnot obtained. When the amount exceeds 80 parts by weight, a coatedarticle having high appearance is not obtained. However, it ispreferable that a pigment is not blended in the coating composition forthe optical member.

In addition, the resin particle (particle of polymer alone) or theinorganic particle (particle of inorganic substance alone) may beblended in the coating composition of this invention in such the rangethat the effect of this invention is not deteriorated.

Then, the coated article in which the coating composition is coated onvarious substrates will be described.

The coated article of this invention is characterized in that theaforementioned coating composition is coated on various substrates. Inaddition, the optical member is characterized in that the aforementionedcoating composition is coated on various transparent substrates.

Examples of the substrate include metals (iron, aluminum, zinc and thelike), timbers, plastics, glasses, slates, mortars, stone materials,concretes and the like. Specific examples include members constitutingautomobiles or home electrical appliances, transparent members such aslight guide plates, and substrates constituting construction materials,miscellaneous goods, papers, and construction wall materials, and thelike.

As the transparent substrate, substrates made of glasses or plastics arepreferable, and examples include substrates made of quartz glass, sodaglass, polycarbonate, polymethyl methacrylate, polyvinyl chloride,polyester, cellulose acetate butyrate, polyolefin, polystyrene, fluorineresin, epoxy resin, polyacrylate, silicone, polyethylene terephthalate,cycloolefin polymer, polyimide and the like.

It is preferable that these substrates have heat resistance, curlingresistance, solvent resistance and the like.

The shape of the substrate, in particular, the transparent substrate ispreferably sheet-like. It is usually preferable that the sheet-likesubstrate has a thickness of about 10 to 3000 μm. The transparentsubstrate constituting an optical sheet as the optical member haspreferably a thickness of 10 to 300 μm.

As a method of coating the coating composition on the substrate, inparticular, the transparent substrate, the known coating method can beselected. For example, coating methods such reverse roll coating method,die coating method, comma coater method, spray coating method, gravurecoating method, rod coating method, and brush coating, roller coating,spray coating, cation electrocoating, electrostatic coating and the likecan be adopted.

The thickness of the coated article is preferably 1 to 500 μm, morepreferably 1 to 200 μm, in the dry state where the solvent has beencompletely volatilized. In particular, in the optical sheet, thethickness of 1 to 100 μm is preferable.

In the optical sheet as the optical member of this invention, thecoating composition may be coated on one side of the sheet-liketransparent substrate, or may be coated on both sides. In addition, aplurality of layers may be formed, each layer being the coated articleon which the coating composition is coated. Furthermore, a hard coatedlayer may be laminated on a surface of the coated article for thepurpose of preventing a flaw or improving weather resistance.

In addition, the light diffusible molded article of this inventioncontains a transparent resin and the aforementioned polymer particlecoated with silica. For this reason, the light diffusible molded articlewhich is excellent in light diffusibility and in which reduction in atotal light transmittance is small can be obtained as compared with thecase where the inorganic particle or the resin particle such aspolyacrylate resin and polystyrene resin is used. Further, compatibilitybetween the polymer particle coated with silica and a transparent resinis better, and more sufficient transparency can be maintained. Inaddition, as compared with the case where the composite particle inwhich a surface of the polymer particle is completely coated with thesilica film is used, complicated light reflection and refraction occur,and more excellent light diffusibility can be manifested. In addition, adiffused light transmittance can be 80% or more. Therefore, for example,in a liquid crystal display using the light diffusible molded article ofthis invention, since loss of light from a backlight can be decreased,consumed electric power can be suppressed.

Herein, the term “transparent” includes “semi-transparent”. Further,“transparent” is not necessarily required to be transparent to light inall wavelength, but is enough that light of at least a particularwavelength can be transmitted. Light includes not only visible light butalso ultraviolet light and infrared light.

In this invention, the amount of the aforementioned polymer particlecoated with silica to be blended is preferably 0.1 to 20 parts by weightper 100 parts by weight of the aforementioned transparent resin (100parts by weight of the resin component except for various additives suchas ultraviolet absorbing agent).

When the amount is in this range, the light diffusible molded articlewhich is excellent in light diffusibility, and has small reduction in atotal light transmittance and, moreover, has a diffused lighttransmittance of 80% or more, can be more assuredly obtained. Asdescribed above, the light diffusible molded article of this inventionhas an advantage that light diffusibility is excellent, and reduction ina total light transmittance is small and, moreover, a transmittance ofdiffused light is high.

Then, a preferable embodiment of the light diffusible molded article ofthis invention will be described with reference to the drawings.

The light diffusible molded article of this invention is characterizedin that polymer particles coated with silica 3 of FIG. 1 are blended inthe transparent resin 4 as exemplified in FIG. 4, and it is preferablethat a value of a diffused light transmittance represented by,diffused light transmittance (%)=total light transmittance (%)×haze(%)×0.01,  (equation)is 80% or more.

In the light diffusible molded article of this invention, a ratio of thepolymer particle coated with silica to be blended is usually 0.1 to 20parts by weight, preferably 0.3 to 15 parts by weight, furtherpreferably 1 to 15 parts by weight, per 100 parts by weight of thetransparent resin. When the blending ratio is more than 30 parts byweight, it becomes difficult to prepare the light diffusible moldedarticle, being not preferable. On the other hand, when the blendingratio is lower than 0.1 parts by weight, it becomes difficult to adjusta diffused light transmittance to 80% or more, being not preferable.

In this invention, as the transparent resin, a thermoplastic resin isusually used, and examples of the thermoplastic resin include(meth)acrylic resin, alkyl (meth)acrylate-styrene copolymer resin,polycarbonate resin, polyester resin, polystyrene resin, polypropyleneresin, polystyrene resin and the like.

Among these, when excellent transparency is required, (meth)acrylicresin, alkyl (meth)acrylate-styrene copolymer resin, polycarbonateresin, and polyester resin are preferable. These thermoplastic resinscan be used alone, or may be used by combining two or more.

As the polymer particle coated with silica, a particle having adifference in a refractive index from the transparent resin in a rangeof preferably 0.01 to 0.1, more preferably 0.02 to 0.1, is used.

When the difference in a refractive index is less than 0.01, asufficient haze is not obtained, and it is not preferable that thediffused light transmittance is less than 80%. On the other hand, whenthe difference in a refractive index is more than 0.1, light diffusingproperty of the molded article becomes too high, and it is notpreferable that a total light transmittance is remarkably reduced.

The minor amount of an additive such as ultraviolet absorbing agent,heat stabilizer, coloring agent, filler or the like may be added to thetransparent resin.

In the light diffusible molded article of this invention, the size andthe shape of the polymer particle coated with silica are notparticularly limited. When the light diffusible molded article is usedas a signboard or a container, the volume-average particle diameter ispreferably 3 to 50 μm. When the light diffusible molded article is usedin the optical component, in particular, the optical component for whichprecision such as precise image display is required in a liquid crystaldisplay or a projection television, the volume-average particle diameteris preferably 3 to 30 μm.

When the diameter is 3 to 50 μm, more uniform diffused light and a hightotal light transmittance are obtained and, in the field in which ahighly precise image such as a display is required, a precise image isobtained in the case of smaller particles of 3 to 30 μm.

In addition to the aforementioned polymer particle coated with silica, aresin particle (particle of resin alone) or an inorganic particle may beblended in the light diffusing molded particle of this invention in suchthe range that the effect of this invention is not deteriorated.

The light diffusing molded particle of this invention is usuallyobtained by mixing the polymer particle coated with silica and thetransparent resin, melting and kneading them, and molding the mixture bya molding method such as extrusion molding and injection molding.

EXAMPLES

Then, this invention will be described in more detail below by way ofexamples, but this invention is not limited by these descriptions.

First, in the examples of this invention, a volume-average particlediameter, Tg, a specular reflectance, an aperture ratio, h/D,re-dispersibility, a haze, a total light transmittance, a diffused lighttransmittance, and a refractive index were measured by the followingmethods.

(Method of Measuring Volume-Average Particle Diameter)

The particle diameter was measured by a coulter counter method.

The coulter counter method is a method of measuring the particlediameter by an electric resistance method called coulter principle.

More particularly, this method is a method in which electrodes areplaced on both sides of an aperture (fine pore) of an aperture tube inan electrolyte solution, a current is passed between both electrodes, aparticle to be measured is suspended in an electrolyte solution, theelectrolyte solution is sucked with a manometer from the interior of theaperture tube and, when the electrolyte solution is passed through theaperture, the electrolyte solution corresponding to the particle volumeis replaced, a resistance is generated between both electrodes and,since a change amount in this resistance is proportionate to the volumeof the particle passing through the aperture, this is detected andcalculated to obtain the volume-average particle diameter of theparticle diameter.

Specifically, according to “REFERENCE MANUAL FOR THE COULTER MULTISIZER”(1987), published by Coulter Electronics Limited, calibration wasperformed using an aperture having the diameter of 100 μm, and thevolume-average particle diameter was measured. More specifically, 0.1 gof particles was pre-dispersed in 10 ml of a 0.1% nonionic surfactantsolution using a touch mixer and an ultrasound employing, as a particlediameter measuring apparatus, an apparatus constructed of CoulterMultisizer II and Sampling Stand IIA (manufactured by Beckman CoulterInc.), this was added to a beaker containing 300 ml of ISOTON II(measuring electrolyte solution, manufactured by Beckman Coulter Inc.)disposed on Sampling Stand II, with a dropper while mildly stirring,this was adjusted so that a densitometer on a body screen indicatesabout 10%, and the volume-average particle diameter of 100 thousands ofparticles was measured.

(Method of Measuring Tg)

Measurement of Tg was performed using TG/DTA6200 (manufactured by SeikoInstruments Inc.).

Measurement

About 0.02 g of a sample was weighed into an aluminum oven container(manufactured by Seiko Instruments Inc.), and this was set in anautosampler of TG/DTA6200. The temperature was raised at 5° C./min, anddifferential thermal analysis was performed at the temperature from roomtemperature (about 25° C.) to 400° C. under the air atmosphere.

Analysis

An inflexion point part of a graph derived from Tg of a polymer wasfound out from a graph (ordinate axis: temperature, abscissa axis: time)obtained by the aforementioned procedure, and the inflexion point wasadopted as a Tg temperature. In the case of the absence of Tg, there isno inflexion point until degradation of a measurement subject begins,and the temperature is risen linearly.

(Method of Measuring Specular Reflectance)

Sample Preparation

A double-sided adhesive tape (NITTO TAPE: manufactured by Nitto DenkoCorp.) was applied to a whole surface a white black covering paper(manufactured by BYK-Gardner GmBH) cut into 50 mm×100 mm, 1 g ofparticles were placed on an adhesive side, particles were spread evenlyin a length direction and a traverse direction every 10 times using acosmetic sponge, extra particles were fallen by blowing a compressed airat 1.5 kg/cm² to a whole surface for 30 seconds from a place at adistance of 20 cm from a sample, and the specular reflectance of a partin which a ground is black is measured.

Measurement

For measuring the specular reflectance, the specular reflectance with anincident light 60° relative to a particle-adhered surface was measuredusing VGS-300A and VGS-SENSOR (manufactured by Nippon DenshokuIndustries Co., Ltd.) according to JIS Z8741. Measurement was performedfive times, and the average value is adopted as the specular reflectanceherein.

This specular reflectance means that as a value grows larger, lightdiffusibility and light reflectivity become poor and, as a value blowssmaller, light diffusibility and light reflectivity are improved.

(Method of Confirming Polymer Particle Coated with Silica)

A method of confirming the polymer particle coated with silica is amethod of adding dropwise one droplet of a dispersion of the polymerparticle coated with silica in water on a slide glass, and observing thepolymer particle coated with silica described in Examples with nakedeyes using a microscope (lens used: magnification 600) with a lightsource of a sodium lamp.

(Method of Measuring Aperture Ratio)

In a method of measuring the aperture ratio, first, 1 g of the polymerparticle coated with silica was weighed into a 50 ml of a porcelaincrucible, this was fired at 500° C. for 2 hours using an electricfurnace (manufactured by ISUZU), and particles composed of only asilica-part of the polymer particle coated with silica (hereinafter,referred to as silica particle) shown in FIG. 2 was obtained.

Then, this silica particle was calmly taken out from a porcelaincrucible with a spater so as not to damage them, and a photograph wastaken with a scanning electron microscope (GMS-820-A: manufactured byJEOL. Ltd.).

Further, among taken photographs, arbitrary 50 in which an opening partof the silica particle is present on an upper side were selected, acontour of the silica particle and a contour of an opening part of eachphotograph manually were designated by using trace measurement of animage analyzing device (Image-Ana LITE: manufactured by Omron Co.,Ltd.), and a projected area (S2) of the silica particle and an area (S1)of an opening part were measured as exemplified in FIG. 3.

From each measured area, the aperture ratio of individual silicaparticles was obtained by the following equation, and the average valueis shown in examples.Aperture ratio=area of opening part of the silica particle(S1)/projected area of the silica particle (S2)(Measurement of h/D of Silica Particle)

As shown in FIG. 2, letting the diameter of the silica particle to be Dand a height of silica particle to be h, the value of h/D was measuredby the following method.

According to the same manner as that of the method of measuring theaperture ratio, a scanning electron micrograph of the silica particlewas taken, among taken photographs, arbitrary 50 particles in which aplane of an opening part of the silica particle was vertical relative toa photograph taking plane were selected. The value of D and the value ofh of individual particles were measured with the image analyzing device,and h/D was calculated. Herein, h/D means the average of 50 h/Ds.

(Assessment of Re-dispersibility)

40 ml of a prepared coating composition was filled into a 50 ml sampletube with a lid, this was centrifuged at 3000 rpm for 10 minutes using acentrifuge to completely separate a liquid part and a solid part, asample tube was set transversely in a rotary shaker (manufactured byTaiyo Scientific Industrial Co., Ltd.), and vibrated for 10 minutesunder vibration condition of 60 times/min.

And, the state after vibration was confirmed with naked eyes, theabsence of a mass of particles was assessed to be ◯, and remaining of amass of particles was assessed to be X.

(Measurement of Total Light Transmittance, Haze, Specular Reflectance,Diffused Light Transmittance)

The total light transmittance and the haze of a coated article and amolded article were measured with a hazemeter (“NDH-2000” manufacturedby Nippon Denshoku Industries Co., Ltd.; according to JIS K7105).

In addition, a specular reflectance at an incident light of 60° relativeto a coated side of a coated article was measured using VGS-300A andVGS-SENSOR (manufactured by Nippon Denshoku Industries Co., Ltd.)according to JIS Z8741. Measurement was performed five times, and theaverage value was adopted as the specular reflectance herein.

Further, a diffused light transmittance is a ratio occupied by diffusedlight among the total light transmittance, and the diffused lighttransmittance was obtained by the equation represented by:Diffused light transmittance (%)=total light transmittance (%)×haze(%)×0.01(Method of Measuring Refractive Index)1. Method of Measuring Refractive Index of Polymer Particle

0.001 g of the polymer particles was placed on a slide glass, and theparticles were dispersed with 0.2 ml of a liquid organic compound havinga refractive index which was arbitrarily selected from the publication“ATAGO Refractometer Databook” (published by ATAGO Co., Ltd.), toprepare a sample plate.

Then, each sample plate was set on an optical microscope, this wasobserved using a sodium lamp as a light source, and disappearance of acontour of particles at a temperature at which a refractive index ofeach liquid organic compound is known was confirmed, and a refractiveindex of a liquid organic compound used thereupon was adopted as arefractive index of particles.

The aforementioned publication describes, as a liquid organic compoundand its refractive index, for example:

Furfurylamine (17° C.) . . . refractive index: 1.4900, and

p-diethylbenzene . . . refractive index: 1.4948,

but as a refractive index, a refractive index obtained by rounding tofour decimal places was adopted. When the temperature is not describedas in p-diethylbenzene, the presence or the absence of a contour ofparticles was confirmed at 20° C.

In the following Preparation Examples, using a monomer composition whichhad been separately prepared as in each Preparation Example, eachmonomer was radical-polymerized to obtain the polymer particle, thepolymer particles were taken out without condensing with a polysiloxaneoligomer, and washed with toluene to completely wash out polysiloxaneoligomer, which was used to measure a refractive index as describedabove.

2. Method of Measuring Refractive Index of Transparent Resin

A transparent resin was ground into particles (about 1 mg or less perone particle), and this was used to measure a refractive index as in thecase of the aforementioned polymer particle.

(Examples and Comparative Examples of Polymer Particle Coated withSilica)

Example 1

A dispersing medium in which 5 g of magnesium pyrophosphate obtained bydouble decomposition as a suspension stabilizer was mixed with 200 g ofwater, was placed into a 500 ml separable flask, and 0.04 g of sodiumlaurylsulfate as a surfactant, and 0.02 g of sodium nitrite as apolymerization inhibitor were dissolved in the dispersing medium.

Separately, 70 g of methyl methacrylate as a monofunctionalpolymerizable vinyl-based monomer, 30 g of MKC silicate MS57(manufactured by Mitsubishi Chemical Co., Ltd.: average molecular weight1300 to 1500, R in the aforementioned structure is methyl, and anaverage of n is 15 to 18) as a polyalkoxysiloxane oligomer, and 0.25 gof 2,2′-azobis(2,4-dimethylvaleronitrile) as a polymerization initiatorwere uniformly dissolved to prepare a monomer composition.

This monomer composition was added to the above dispersing medium, andthis was stirred with a homomixer (ULTRA TURRAX T-25, manufactured byIKA) at 8000 rpm for about 10 seconds to finely disperse the monomercomposition. A stirring wing, a thermometer and a refluxing condenserwere attached to a separable flask, the flask was replaced withnitrogen, and this was mounted in a constant temperature water bath(water bath) at 60° C. The interior of the separable flask was stirredcontinuously at a stirring rate of 200 rpm and, when a temperature of adispersing medium with the monomer composition added thereto in theseparable flask reached 60° C., suspension polymerization was performedfor 10 hours to a polymerizable vinyl-based monomer, and 2 g of sodiumhydroxide was added to condense the polyalkoxysiloxane oligomer.

Then, the separable flask was removed from the constant temperaturewater bath, the reaction solution in the separable flask was cooled toroom temperature while stirring the interior of the separable flask,hydrochloric acid was added to adjust a pH of a slurry to about 2 todecompose a suspension stabilizer, and the polymer particles coated withsilica in which a surface of a polymer particle was exposed wereobtained. The resulting particles were suction-filtered with a Buchnerfunnel using a filter, washed with 1.2 L of ion-exchanged water toremove a suspension stabilizer, and dried to take out objectiveparticle. The volume-average particle diameter of the resulting polymerparticles coated with silica is 5.8 μm, and Tg of a polymer particlederived from the polymerizable vinyl-based monomer is 105° C. Thespecular reflectance, the aperture ratio, h/D and the refractive indexof the particle are shown in Table 1.

Example 2

According to the same manner as that of Example 1 except that an amountof methyl methacrylate was changed to 30 g, an amount of MKC silicateMS57 was changed to 70 g, and an amount of2,2′-azobis(2,4-dimethylvaleronitrile) was changed to 0.15 g, polymerparticles coated with silica in which a surface of a polymer particlewas exposed were obtained. The volume-average particle diameter of theresulting polymer particles coated with silica is 116.3 μm, and Tg of apolymer particle derived from the polymerizable vinyl-based monomer is105° C. The specular reflectance, the aperture ratio, h/D and therefractive index of the particle are shown in Table 1.

Example 3

According to the same manner as that of Example 1 except that, aspolyalkoxysiloxane oligomer, MKC silicate MS 51 (manufactured byMitsubishi Chemical Co., Ltd.: average molecular weight of 500 to 700, Rin the aforementioned structural formula is methyl, and an average of nis 5 to 10) was used, polymer particles coated with silica in which asurface of a polymer particle was exposed were obtained. Thevolume-average particle diameter of the resulting polymer particlescoated with silica is 6.4 μm, and Tg of a polymer part derived from thepolymerizable vinyl-based monomer is 105° C. The specular reflectance,the aperture ratio, h/D and the refractive index of the particle areshown in Table 1.

Example 4

According to the same manner as that of Example 1 except that, aspolyalkoxysiloxane oligomer, MKC silicate MS 58B15 (manufactured byMitsubishi Chemical Co., Ltd.: average molecular weight of 1600 to 1800,R in the aforementioned structural formula is butyl, and an average of nis 11 to 13) was used, polymer particles coated with silica in which asurface of a polymer particle was exposed were obtained. Thevolume-average particle diameter of the resulting polymer particlescoated with silica is 17.1 μm, and Tg of a polymer part derived from thepolymerizable vinyl-based monomer is 105° C. The specular reflectance,the aperture ratio, h/D and the refractive index of the particle areshown in Table 1.

Example 5

According to the same manner as that of Example 1 except that styrenewas used as a polymerizable vinyl-based monomer, polymer particlescoated with silica in which a surface of a polymer particle was exposedwere obtained. The volume-average particle diameter of the resultingpolymer particles coated with silica is 12.5 μm, and Tg of a polymerpart derived from the polymerizable vinyl-based monomer is 84° C. Thespecular reflectance, the aperture ratio, h/D and the refractive indexof the particle are shown in Table 1.

Example 6

According to the same manner as that of Example 1 except that n-butylacrylate was used as a polymerizable vinyl-based monomer, polymerparticles coated with silica in which a surface of a polymer particlewas exposed were obtained. The volume-average particle diameter of theresulting polymer particles coated with silica is 19.5 μm, and Tg of apolymer part derived from the polymerizable vinyl-based monomer is −54°C. The specular reflectance, the aperture ratio, h/D and the refractiveindex of the particle are shown in Table 1.

Comparative Example 1

A dispersing medium in which 18 g of magnesium pyrophosphate obtained bya double decomposition method as a suspension stabilizer had been mixedinto 900 g of water was placed into a 2-L stainless beaker, and 0.18 gof sodium laurylsulfate as a surfactant, and 0.1 g of sodium nitrite asa polymerization inhibitor were dissolved in the dispersing medium.

Separately, 270 g of methyl methacrylate as a monofunctionalpolymerizable vinyl-based monomer, 30 g of dimethacrylic acid ethyleneglycol, and 0.3 g of azobisisobutyronitrile as a polymerizationinitiator were uniformly dissolved to prepare a monomer composition.

This monomer composition was added to the aforementioned dispersingmedium, this was stirred with a homomixer (TK homomixer manufactured byTokushu Kika Kogyo Co. Ltd.) at 4000 rpm for about 10 seconds to finelydisperse the monomer-composition. The dispersing medium was placed intoa polymerization machine equipped with a stirrer and a thermometer, andstirring was continued at 50° C. for 5 hours to complete suspensionpolymerization.

After cooling, hydrochloric acid was added to a suspension, thesuspension stabilizer was degraded, and the polymer particle wasisolated, washed with water, and dried under reduced pressure to obtainspherical polymer particles (volume-average particle diameter: 13.1 μm).Since the spherical polymer particle had a crosslinked structure, Tg wasnot confirmed until 260° C. at which degradation of the particle byheating began.

21 g of the spherical polymer particles and 9 g of Aerosil R972(manufactured by Aerosil, volume-average particle diameter: 16 nm) weretreated with a hybridizer (manufactured by Nara Kikai Kogyo Co., Ltd.)at 50° C. and 14000 rpm for 5 minutes to obtain composite particleshaving a surface coated with the silica particle (volume-averageparticle diameter: 13.6 μm). The specular reflectance and the refractiveindex of the particle are shown in Table 1.

Comparative Example 2

According to the same manner as that of Example 1 except that an amountof methyl methacrylate was changed to 97 g, and an amount of MKCsilicate MS57 was changed to 3 g, and an amount of 2,2′-azobis(2,4-dimethylvaleronitrile) was changed to 0.45 g, polymer particlescoated with silica in which a surface of a polymer particle was exposedwere obtained. The volume-average particle diameter of the resultingpolymer particles coated with silica is 15 μm, and Tg of a polymer partderived from a polymerizable vinyl-based monomer is 105° C. Since theresulting particle had a small region coated with silica, a silica filmwas peeled in some cases. The specular reflectance, the aperture ratio,h/D and the refractive index of the particles are shown in Table 1.

Example 7

According to the same manner as that of Example 1 except that apolymerizable vinyl-based monomer was changed to 56 g of methylmethacrylate and 14 g of ethylene glycol dimethacrylate, polymerparticles coated with silica in which a surface of a polymer particlewas exposed were obtained. The volume-average particle diameter of theresulting polymer particles coated with silica is 15 μm, and Tg of apolymer part derived from a polymerizable vinyl-based monomer could notbe confirmed until 260° C. at which the particle began to be degraded byheating because that part had a crosslinked structure. The specularreflectance, the aperture ratio, h/D and the refractive index of theparticles are shown in Table 1.

Example 8

According to the same manner as that of Example 7 except that methylmethacrylate was changed to styrene, and ethylene glycol dimethacrylatewas changed to divinylbenzene, polymer particles coated with silica inwhich a surface of a polymer particle was exposed were obtained. Thevolume-average particle diameter of the polymer particles coated withsilica is 6 μm, and Tg of a polymer part derived from a polymerizablevinyl-based monomer could not be confirmed until 260° C. at whichparticles began to be degraded by heating because that part had acrosslinked structure. The specular reflectance, the aperture ratio, h/Dand the refractive index of the particle are shown in Table 1.

Example 9

According to the same manner as that of Example 7 except that MKCsilicate MS 58 B15 (manufactured by Mitsubishi Chemical Co., Ltd.,average molecular weight of 1600 to 1800) was used as apolyalkoxysiloxane oligomer, and stirring condition with a homomixer wasat 10000 rpm for about 10 seconds, polymer particles coated with silicain which a surface of a polymer particle was exposed were obtained. Thevolume-average particle diameter of the polymer particles coated withsilica is 5 μm, and Tg of a polymer part derived from a polymerizablevinyl-based monomer could not be confirmed until 260° C. at which theparticle began to be degraded by heating because that part had acrosslinked structure. The specular reflectance, the aperture ratio, h/Dand the refractive index of the particle are shown in Table 1.

Example 10

According to the same manner as that of Example 7 except that an amountof magnesium pyrophosphate was 7.5 g, and an amount of sodiumlaurylsulfate as a surfactant was 0.06 g, and stirring condition with ahomomixer was at 10000 rpm for 60 seconds, polymer particles coated withsilica in which a surface of a polymer particle was exposed wereobtained. The volume-average particle diameter of the polymer particlescoated with silica is 3 μm, and Tg of a polymer part derived from apolymerizable vinyl-based monomer could not be confirmed until 260° C.at which particles began to be degraded by heating because that part hada cross-linked structure. The specular reflectance, the aperture ratio,h/D and the refractive index of the particle are shown in Table 1.

Example 11

According to the same manner as that of Example 7 except that 56 g ofstyrene was changed to 28 g of styrene and 28 g of methyl methacrylate,polymer particles coated with silica in which a surface of a polymerparticle was exposed were obtained. The volume-average particle diameterof the polymer particles coated with silica is 6 μm, and Tg of a polymerpart derived from a polymerizable vinyl-based monomer could not beconfirmed until 260° C. at which the particle began to be degraded byheating because that part had a crosslinked structure. The specularreflectance, the aperture ratio, h/D and the refractive index of theparticle are shown in Table 1.

Comparative Example 3

500 g of deionized water in which 0.05 g of sodium laurylsulfate hadbeen dissolved was placed into a polymerization vessel equipped with astirrer and a thermometer, and 50 g of calcium tertiary phosphate wasadded to be dispersed. Into the dispersion was placed a mixed solutionin which 0.5 g of benzoyl peroxide and 0.5 g of azobisisobutyronitrilewere dissolved in 85 g of styrene and 15 g of divinylbenzene which are apolymerizable vinyl monomer, and the materials were dispersed with a T.Khomomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) to adjustdroplets to about 6 μm. Then, the interior of a polymerization vesselwas heated to 65° C. to perform suspension polymerization whilestirring, followed by cooling. The suspension was filtered, washed anddried to obtain spherical polymer particles. The volume-average particlediameter of the resulting polymer particles is 6 μm, and Tg of a polymerparticle derived from a polymerizable vinyl-based monomer could not beconfirmed until 260° C. at which particles began to be degraded byheating because that part had a crosslinked structure. The specularreflectance, the aperture ratio, h/D and the refractive index of theparticle are shown in Table 1.

Comparative Example 4

According to the same manner as that of Comparative Example 3 exceptthat styrene was changed to methyl metahcrylate, divinylbenzene waschanged to ethylene glycol dimethacrylate, and a particle diameter ofdroplets was changed to about 15 μm, spherical polymer particles wereobtained. The volume-average particle diameter of the polymer particlesis 15 μm and Tg of a polymer part derived from a polymerizablevinyl-based monomer could not be confirmed until 260° C. at whichparticles began to be degraded by heating because that part had acrosslinked structure. The specular reflectance, the aperture ratio, h/Dand the refractive index of the particle are shown in Table 1.

Comparative Example 5

(Preparation of Solution of Polymer in Toluene)

144.5 g of tetramethoxysilane, 23.6 g ofγ-methacryloxypropyltrimethoxysilane, 19 g of water, 30 g of methanoland 5 g of Amberlist 15 (cation exchange resin manufactured by Rohm andHaas Japan) were charged into a 300 ml four-neck flask equipped with astirrer, a thermometer and a condenser, and the materials were stirredat 65° C. for 2 hours to react them. The reaction mixture was cooled toroom temperature, a distillation tower was attached in place of acondenser, this was provided with a condenser and an efflux port, atemperature was raised to 80° C. for 2 hours under the atmosphericpressure, and a temperature was retained at the same temperature untilmethanol did not come out, to further proceed the reaction. After cooledto room temperature again, Amberlist 15 was filtered to obtainpolymerizable polysiloxane having the number average molecular weight of1800.

Then, 200 g of toluene as an organic solvent was placed into a 1 literflask equipped with a stirrer, an addition port, a thermometer, acondenser and a nitrogen gas introducing port, a nitrogen gas wasintroduced, and the flask was heated to an internal temperature of 110°C. while stirring. Then, a solution obtained by mixing 20 g of thepolymerizable polysiloxane obtained as described above, 80 g of methylmethacrylate, 10 g of 2-ethylhexyl acrylate, 60 g of styrene, 30 g ofbutyl acrylate and 6 g of 2,2′-azobisisobutyronitrile was added dropwisethrough the addition port over 2 hours. After addition, stirring wascontinued at the same temperature for 1 hour, 0.4 g of1,1′-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane was added two timesevery 30 minutes, and the materials were heated for 2 hours to performcopolymerization, to obtain a solution of a polymer in toluene in whicha polymer having the number average molecular weight of 12000 wasdissolved in toluene. A solid matter in the resulting solution was 49.5%by weight.

(Preparation of Dispersion)

496 g of butyl acetate and 124 g of methanol were placed into a 1 literfour-neck flask equipped with a stirrer, two addition ports (additionports 1 and 2) and a thermometer, and an internal temperature wasadjusted to 20° C. Then, a mixed solution (solution A) of 10 g of theabove-obtained solution of the polymer in toluene and 100 g oftetramethoxysilane, and a mixed solution (solution B) of 30 g of water,30 g of 25% aqueous ammonia and 60 g of methanol were added dropwisethrough the addition port 1 and the addition port 2, respectively, over1 hour while stirring the interior of the flask. After addition,stirring was continued for 2 hours at the same temperature. Then, amixed solution of 37 g of the solution of the polymer in tolueneobtained as described above and 37 g of butyl acetate was added dropwisethrough the addition port 1 over 1 hour. After addition, stirring wascontinued at the same temperature for 2 hours. Further, an interiortemperature of the flask was raised to 100° C. under a pressure of 110mmHg, and ammonia, methanol, toluene and butyl acetate were distilledoff until a solid matter concentration became 30% by weight, to obtain adispersion in which the polymer and silica fine particles were dispersedin butyl acetate. The dispersion was diluted with ion exchanged water toa solid contend of about 1% by weight, and the average particle diameter(volume diameter) of the resulting fine particles was measured with alaser diffraction/diffusion-type particle size distribution measuringapparatus (trade name “LS230” manufactured by Coulter Inc.), and wasfound to be 0.18 μm (180 nm).

(Preparation of Silica Composite Polymer Particle)

900 g of deionized water in which 0.5 g of polyvinyl alcohol (PVA-205manufactured by Kuraray Co., Ltd.) had been dissolved was placed into aflask equipped with a stirrer, an inert gas introducing tube, arefluxing condenser and a thermometer. Then, a mixture obtained byblending 75 g of methyl methacrylate, 19 g of ethylene glycoldimethacrylate, 20 g of the above-obtained dispersion and 1 g ofazobisisobutyronitrile was placed into a flask, and this was stirredwith a T.K. homogenizer (manufactured by Tokushu Kika Kogyo Co., Ltd.)at 3000 rpm for 5 minutes to prepare a uniform suspension.

Then, the suspension was heated to 75° C. while blowing into a nitrogengas, stirring was continued at this temperature for 5 hours to perform apolymerization reaction, the reaction mixture was cooled, and thesuspension was filtered, washed and dried to obtain composite particles.The composite particles had a structure in which silica particle wasdispersed in a polymer particle derived from a polymerizable vinylmonomer. The volume-average particle diameter of the polymer particlesis 12 μm, and Tg of a polymer part derived from a polymerizablevinyl-based monomer could not be confirmed until 260° C. at which theparticle began to be degraded by heating because that part had acrosslinked structure. The specular reflectance of the particle is shownin Table 1.

Comparative Example 6

According to the same manner as that of Comparative Example 4 exceptthat a particle diameter of droplets was adjusted to about 5 μm, polymerparticles were obtained. The volume-average particle diameter of thepolymer particles is 5 μm, and Tg of a polymer part derived from apolymerizable vinyl-based monomer could not be confirmed until 260° C.at which particles began to be degraded by heating because that part hada crosslinked structure. The specular reflectance, the aperture ratio,h/D and the refractive index of the particle are shown in Table 1.

Comparative Example 7

According to the same manner as that of Comparative Example 4 exceptthat 5 g of lipophilic Smectite (trade name “SAN” manufactured by CoapChemical) was uniformly dispersed in the monomer composition ofComparative Example 4, and a particle diameter of droplets was adjustedto about 6 μm (stirring condition with a homomixer was at 10000 rpm for10 seconds), Smectite-dispersed composite particles were obtained. Thevolume-average particle diameter of the resulting polymer particles is 6μm, and Tg of a polymer part derived from a polymerizable vinyl-basedmonomer could not be confirmed until 260° C. at which particles began tobe degraded by heating because that part had a crosslinked structure.The specular reflectance, the aperture ratio, h/D and the refractiveindex of the particle are shown in Table 1.

Example 12

According to the same manner as that of Example 7 except thatdivinylbenzene was used in place of ethylene glycol dimethacrylate,polymer particles coated with silica in which a surface of a polymerparticle was exposed were obtained. The volume-average particle diameterof the resulting polymer particle is 20 μm, and Tg of a polymer partderived from a polymerizable vinyl-based monomer could not be confirmeduntil 260° C. at which particles began to be degraded by heating becausethat part had a crosslinked structure. The specular reflectance, theaperture ratio, h/D and the refractive index of the particle are shownin Table 1.

Example 13

According to the same manner as that of Example 7 except that 56 g ofstyrene and 20 g of divinylbenzene were used as a polymerizable vinylmonomer, polymer particles coated with silica in which a surface of apolymer particle was exposed were obtained. The volume-average particlediameter of the resulting polymer particles is 12 μm, and Tg of apolymer part derived from a polymerizable vinyl-based monomer could notbe confirmed until 260° C. at which particles began to be degraded byheating because that part had a crosslinked structure. The specularreflectance, the aperture ratio, h/D and the refractive index of theparticle are shown in Table 1.

Example 14

According to the same manner as that of Example 12 except that MKCsilicate MS58B15 (manufactured by Mitsubishi Chemical Co., Ltd.: averagemolecular weight 1600 to 1800) was used as a polyalkoxysiloxaneoligomer, polymer particles coated with silica in which a surface of apolymer particle was exposed were obtained. The volume-average particlediameter of the resulting polymer particles is 15 μm, and Tg of apolymer part derived from a polymerizable vinyl-based monomer could notbe confirmed until 260° C. at which particles began to be degraded byheating because that part had a crosslinked structure. The specularreflectance, the aperture ratio, h/D and the refractive index of theparticle are shown in Table 1.

Comparative Example 8

500 g of deionized water in which 0.05 g of sodium laurylsulfate hadbeen dissolved was placed in a polymerization vessel equipped with astirrer and a thermometer, and 50 g of tri calcium phosphate was addedto disperse the material. Then, a mixed solution obtained by dissolving0.5 g of benzoyl peroxide and 0.5 g of azobisisobutyronitrile in 80 g ofstyrene and 20 g of divinylbenzene which are a polymerizable vinylmonomer was placed in the polymerization vessel, and the materials weredispersed with a T.K homomixer (manufactured by Tokushu Kika Kogyo Co.,Ltd.) to adjust droplets to about 12 μm. Then, the interior of thepolymerization vessel was heated to 65° C. to perform suspensionpolymerization while stirring, followed by cooled. The suspension wasfiltered, washed and dried to obtain spherical polymerization particles.The volume-average particle diameter of the resulting polymer particlesis 12 μm, Tg of a polymer part derived from a polymerizable vinyl-basedmonomer could not be confirmed until 260° C. at which particles began tobe degraded by heating because that part had a crosslinked structure.The specular reflectance, the aperture ratio, h/D and the refractiveindex of the particle are shown in Table 1.

Comparative Example 9

According to the same manner as that of Comparative Example 8 exceptthat a polymerizable vinyl monomer was changed to 80 g of methylmethacrylate and 20 g of divinylbenzene, spherical polymer particleswere obtained. The volume-average particle diameter of the resultingpolymer particles is 20 μm, and Tg of a polymer part derived from apolymerizable vinyl-based monomer could not be confirmed until 260° C.at which the particle began to be degraded by heating because that parthad a crosslinked structure. The specular reflectance, the apertureratio, h/D and the refractive index of the particle are shown in Table1.

Example 15

According to the same manner as that of Example 13 except that, after apolymer particle part was polymerized as in Example 13, a catalyst forcuring a polyalkoxysiloxane oligomer was changed from 2 g of sodiumhydroxide to 2 g of sodium sulfamate which is an acid, and the curingtemperature was 80° C., polymer particles coated with silica in which asurface of a polymer particle was exposed were obtained. Thevolume-average particle diameter of the resulting polymer particles is20 μm, and Tg of a polymer particle derived from a polymerizablevinyl-based monomer could not be confirmed until 260° C. at whichparticles began to be degraded because that part had a crosslinkedstructure. The specular reflectance, the aperture ratio, h/D and therefractive index of the particle are shown in Table 1.

Example 16

According to the same manner as that of Example 13 except that 56 g ofmethyl methacrylate and 14 g of divinylbenzene were changed to 35 g ofmethyl methacrylate, 21 g of styrene and 14 g of ethylene glycoldimethacrylate, polymer particles coated with silica in which a surfaceof a polymer particle was exposed were obtained. The volume-averageparticle diameter of the resulting polymer particles is 20 μm, and Tg ofa polymer part derived from a polymerizable vinyl-based monomer couldnot be confirmed until 26° C. at which particles began to be degraded byheating because that part had a crosslinked structure. The specularreflectance, the aperture ratio, h/D and the refractive index of theparticle are shown in Table 1.

Example 17

According to the same manner as that of Example 13 except that an amountof methyl methacrylate was 20 g, an amount of divinylbenzene was 5 g, anamount of a polyalkoxysiloxane oligomer was 75 g, and 4 g of sodiumchloride was added to water which is a dispersing medium, polymerparticles coated with silica in which a surface of a polymer particlewas exposed were obtained. The volume-average particle diameter of theresulting polymer particles is 15 μm, and Tg of a polymer part derivedfrom a polymerizable vinyl-based monomer could not be confirmed until260° C. at which particles began to be degraded by heating because thatpart had a crosslinked structure. The specular reflection, the apertureratio, h/D and the refractive index of the particle are shown in Table1.

TABLE 1 specular aperture refractive reflection(%) ratio h/D index  EX.111.3 0.56 0.78 1.490  EX.2 10.6 0.16 0.92 1.490  EX.3 11.7 0.61 0.721.490  EX.4 11.9 0.69 0.70 1.490  EX.5 9.6 0.58 0.77 1.590  EX.6 10.90.52 0.79 1.480  EX.7 10.9 0.55 0.79 1.490  EX.8 9.5 0.59 0.76 1.590 EX.9 11.1 0.61 0.73 1.490 EX.10 11.7 0.62 0.72 1.490 EX.11 10.2 0.600.69 1.530 EX.12 10.1 0.65 0.64 1.510 EX.13 9.9 0.48 0.65 1.590 EX.1411.5 0.63 0.74 1.510 EX.15 9.8 0.67 0.67 1.510 EX.16 10.4 0.72 0.781.520 EX.17 10.4 0.18 0.93 1.510 COM. EX.1 14.7 — — 1.490 COM. EX.2 15.11 0.36 1.490 COM. EX.3 13.7 — — 1.590 COM. EX.4 15.0 — — 1.490 COM. EX.514.5 — — 1.510 COM. EX.6 14.7 — — 1.490 COM. EX.7 14.4 — — 1.490 COM.EX.8 13.7 — — 1.590 COM. EX.9 14.1 — — 1.510 Silica particle 16.9 — — —Silica particle: TOKUSEAL U (made by Tokuyama Corp., particle diameter:14 μm)

From Examples 1 to 17 and Comparative Examples 1 to 9, the following canbe seen.

From Examples 1 to 6 and Comparative Example 1, when a polymer particlecoated with silica in which a surface of a polymer particle is exposed,and a polymer particle coated with silica in which the surface is notexposed are compared, it is seen that the former has small specularreflectance, and has excellent light diffusibility and reflectivity asshown in Table 1.

From Comparative Example 2, it is seen that when a region of a silicafilm covering the polymer particle is small, a silica film is peeled,and sufficient light diffusibility and reflectivity are not obtained.

From Example 6, it is seen that the method of this invention is notlimited to a kind of the polymer particle, but even when Tg is low, thepolymer particle coated with silica can be provided.

From Examples 7 to 17, it is seen that, even when the polymer particleis crosslinked, the polymer particle coated with silica can be provided.

From Examples 7 to 17 and Comparative Examples 3 to 4, and 6 to 9, it isseen that, by having a silica film, excellent light diffusibility andreflectivity are possessed.

From Examples 7 to 11 and Comparative Example 5, it is seen thatparticles in which a silica film is formed has more excellent lightdiffusibility and reflectivity than the case where the silica particleis dispersed.

From Examples 1 to 17, it is seen that the silica particle in which avalue of h/D is in a range of 0.5≦h/D<1 have suitable diffusibility andreflectivity. When a value of h/D is less than 0.5, a silica film iseasily peeled from the polymer particle and, when a value of h/D is 1,light diffusibility and reflectivity become poor.

Examples and Comparative Examples of Coating Composition Example 18

100 parts by weight of the polymer particles coated with silica preparedin Example 7 was blended in a binder solution in which 100 parts byweight of a polyacrylate resin (trade name “BR106”, manufactured byMitsubishi Rayon Co., Ltd.) as a binder resin had been dissolved in 300parts by weight of a solvent (toluene 180 parts by weight, ethyl acetate90 parts by weight, butyl acetate 30 parts by weight), and the materialswere uniformly dispersed to prepare a coating composition.

This coating composition was coated on a polyethylene terephthalate filmhaving a thickness of 100 μm which is a transparent substrate using a 75μm applicator, and dried to prepare a light diffusing sheet.

The haze and the total light transmittance of a surface of this lightdiffusing sheet were measured by the aforementioned methods,respectively. The results are shown in the following Table 2.

Example 19

According to the same manner as that of Example 18 except that 20 partsby weight of the polymer particles coated with silica obtained inExample 8 was used, a light diffusing sheet was prepared. The haze andthe total light transmittance of a surface of the resulting lightdiffusing sheet were measured. The results are shown in the followingTable 2.

Example 20

According to the same manner as that of Example 18 except that 70 partsby weight of the polymer particles coated with silica obtained inExample 10 was used, a light diffusing sheet was prepared. The haze andthe total light transmittance of a haze of surface of the resultinglight diffusing sheet were measured. The results are shown in thefollowing Table 2.

Example 21

According to the same manner as that of Example 18 except that anaddition amount of the polymer particles coated with silica to be addedwas changed to 150 parts by weight, a light diffusing sheet wasprepared. The haze and the total light transmittance of a surface of theresulting light diffusing sheet were measured. The results are shown inthe following Table 2.

Comparative Example 11

According to the same manner as that of Example 18 except that thepolymer particles obtained in Comparative Example 3 were used at anamount of 3 g per 300 g of a methyl methacrylate resin in place of thepolymer particles coated with silica, a light diffusing sheet wasobtained. The haze and the total light transmittance of a surface of theresulting light diffusing sheet were measured. The results are shown inthe following Table 2.

Comparative Example 12

According to the same manner as that of Example 18 except that thepolymer particles obtained in Comparative Example 4 were used in placeof the polymer particles coated with silica, a light diffusing sheet wasobtained. And, the haze and the total light transmittance of a surfaceof the resulting light diffusing sheet were measured. The results areshown in the following Table 2.

Comparative Example 13

According to the same manner as that of Example 18 except that thepolymer particles coated with silica obtained in Comparative Example 5were used, a light diffusing sheet was obtained. And, the haze and thetotal light transmittance of a surface of the resulting light diffusingsheet were measured. The results are shown in the following Table 2.

Comparative Example 14

According to the same manner as that of Example 18 except that thepolymer particles coated with silica obtained in Comparative Example 7were used, a light diffusing sheet was obtained. And, the haze and thetotal light transmittance of a surface of the resulting light diffusingsheet were measured. The results are shown in the following Table 2.

TABLE 2 haze total light (%) transmittance(%) EX.18 94.11 88.55 EX.1994.36 86.75 EX.20 95.12 86.02 EX.21 94.53 85.78 COM. EX.11 0.54 96.28COM. EX.12 92.66 81.12 COM. EX.13 91.32 83.21 COM. EX.14 93.23 80.87

As recognized from Comparative Examples 11 to 14 in Table 2, usually,when the haze is increased, the total light transmittance is decreasedand, when the total light transmittance is increased, the haze isdecreased (in particular, Comparative Example 11). That is, usually,increase in the haze means reduction in the total light transmittance,and increase in the total light transmittance means reduction in thehaze.

However, as apparent from comparison with Comparative Examples 12 to 14,in the optical sheets of Examples 18 to 21, both of the haze and thetotal light transmittance are improved than those of ComparativeExamples.

As apparent from this, by using a polymer particle coated with silica inwhich a silica film is provided so as to expose the polymer particle asa particle to be blended in a coating composition, the resulting opticalsheet (optical member) can be excellent in both of the lightdiffusibility (haze) and the total light transmittance. Therefore, it isrecognized that this is suitable in a light diffusing sheet, forexample, a light diffusing sheet which is disposed between a prism sheetand a light guide plate in a liquid crystal display device.

Example 22

10 parts by weight of the polymer particles coated with silica preparedin Example 9 was blended in a binder solution obtained by dissolving 100parts by weight of a polyester resin (trade name “Biron 200”manufactured by Toyobo Co., Ltd.) which is a binder resin in 300 partsby weight of a solvent (toluene 180 parts by weight, ethyl acetate 90parts by weight, butyl acetate 30 parts by weight), and the materialswere uniformly dispersed to prepare a coating composition.

This coating composition was coated on a polyethylene terephthalate filmhaving a thickness of 100 μm which is a transparent substrate using a 20μm applicator, and dried to obtain an antiglare sheet. And, the haze,the total light transmittance and the specular reflectance of a surfaceof the resulting antiglare sheet were measured. The results are shown inthe following Table 3.

Example 23

According to the same manner as that of Example 22 except that 5 partsby weight of the polymer particles coated with silica obtained inExample 10 was used, an antiglare sheet was obtained. And, the haze, thetotal light transmittance and the specular reflectance of a surface ofthe resulting antiglare sheet were measured. The results are shown inthe following Table 3.

Example 24

According to the same manner as that of Example 22 except that 20 partsby weight of the polymer particles coated with silica obtained inExample 11 was used, an antiglare sheet was obtained. And, the haze, thetotal light transmittance and the specular reflectance of a surface ofthe resulting antiglare sheet were measured. The results are shown inthe following Table 3.

Comparative Example 15

According to the same manner as that of Example 22 except that thepolymer particles obtained in Comparative Example 6 were used in placeof the polymer particles coated with silica used in Example 22, anantiglare sheet was obtained. And, the haze, the total lighttransmittance and the specular reflectance of a surface of the resultingantiglare sheet were measured. The results are shown in the followingTable 3.

Comparative Example 16

According to the same manner as that of Example 22 except that thepolymer particles coated with silica obtained in Comparative Example 5were used, an antiglare sheet was obtained. And, the haze, the totallight transmittance and the specular reflectance of a surface of theresulting antiglare sheet was measured. The results are shown in thefollowing Table 3.

Comparative Example 17

According to the same manner as that of Example 22 except that thepolymer particles coated with silica obtained in Comparative Example 7were used, an antiglare sheet was obtained. And, the haze, the totallight transmittance and the specular reflectance of surface of theresulting antiglare sheet were measured. The results are shown in thefollowing Table 3.

TABLE 3 haze total light specular (%) transmittance(%) reflectance(%)EX.22 32.56 92.76 20.45 EX.23 33.72 92.45 25.37 EX.24 34.17 91.78 21.69COM. EX.15 30.21 90.81 42.34 COM. EX.16 30.21 90.93 38.22 COM. EX.1731.22 89.97 33.64

As apparent from Table 3, in optical sheets of Examples 22 to 24, bothof the haze and the total light transmittance are improved than those ofComparative Examples. Moreover, the specular reflectance is considerablyreduced.

As apparent from this, by using the polymer particle coated with silicain which a silica film is provided so as to expose a polymer particle asa particle to be blended in a coating composition, the resulting opticalsheet (optical member) is excellent in both of the light diffusibility(haze) and the total light transmittance and, moreover, can have verysmall specular reflectance. Therefore, it is recognized that this issuitable in an antiglare sheet, for example, an antiglare sheet disposedon the superficialmost side in a liquid crystal display device.

Example 25

50 parts by weight of the polymer particle coated with silica obtainedin Example 7 was blended in 400 parts by weight of an aqueous bindersolution (trade name “Bironal MD1200”, manufactured by Toyobo Co., Ltd.)(binder resin about 30 parts by weight) using a polyester resin as abinder resin, and water and alcohol as a solvent, and the materials wereuniformly dispersed to obtain a coating composition. This coatingcomposition was coated on a white black covering paper (manufactured byBYK-Garder) using a 75 μm applicator, and dried to prepare a coatedarticle. And, the specular reflectance of a surface of the resultingcoated article was measured.

In addition, re-dispersibility of the prepared coating composition wasassessed. The results are shown in the following Table 4.

Example 26

According to the same manner as that of Example 25 except that 10 partsby weight of the polymer particles coated with silica obtained inExample 8 was used, a coating composition was prepared. In addition, asin Example 25, measurement of the specular reflectance and assessment ofre-dispersibility were performed. The results are shown in the followingTable 4.

Example 27

According to the same manner as that of Example 25 except that 100 partsby weight of the polymer particles coated with silica obtained inExample 11 was used, a coating composition was prepared. In addition, asin Example 25, measurement of the specular reflectance and assessment ofre-dispersibility were performed. The results are shown in the followingTable 4.

Comparative Example 18

According to the same manner as that of Example 24 except that 10 partsby weight of the polymer particles obtained in Comparative Example 4 wasused in place of the polymer particle coated with silica used in Example25, a coating composition was prepared. In addition, as in Example 25,measurement of the specular reflectance and assessment ofre-dispersibility were performed. The results are shown in the followingTable 4.

Comparative Example 19

According to the same manner as that of Example 25 except that 10 partsby weight of the polymer particles coated with silica obtained inComparative Example 5 was used, a coating composition was prepared. Inaddition, as in Example 25, measurement of the specular reflectance andassessment of re-dispersibility were performed. The results are shown inthe following Table 4.

Comparative Example 20

According to the same manner as that of Example 25 except that thepolymer particles coated with silica were not blended, a coatingcomposition was prepared. In addition, as in Example 25, measurement ofthe specular reflectance was performed. The results are shown in thefollowing Table 4.

Comparative Example 21

According to the same manner as that of Example 25 except that 20 partsby weight of the polymer particles coated with silica obtained inComparative Example 7 was used, a coating composition was prepared. Inaddition, as in Example 25 measurement of the specular reflectance andassessment of re-dispersibility were performed. The results are shown inthe following Table 4.

Example 28

50 parts by weight of the composite particles obtained in Example 1 wasblended in 400 parts by weight of an aqueous binder solution (trade name“Bironal MD1200”, manufactured by Toyobo Co., Ltd.) (binder resin about120 parts by weight) using a polyester resin as a binder resin, andwater and alcohol as a solvent, and the materials were uniformlydispersed to prepare a coating composition. This coating composition wascoated on a white black covering paper (manufactured by BYK-Garder)using a 75 μm applicator, and dried to prepare a coated article. And,the specular reflectance of a surface of the resulting coated articlewas measured.

In addition, assessment of dispersibility of the prepared coatingcomposition was performed. The results are shown in the following Table4.

Example 29

According to the same manner as that of Example 28 except that 50 partsby weight of the particles of Example 3 was used, a coated article wasprepared. And, the specular reflectance of a surface of the resultingcoated article was measured.

In addition, assessment of dispersibility of the prepared coatingcomposition was performed. The results are shown in the following Table4.

Example 30

According to the same manner as that of Example 28 except that 50 partsby weight of the particles of Example 4 was used, a coated article wasprepared. And, the specular reflectance of a surface of the resultingcoated article was measured.

In addition, assessment of dispersibility of the prepared coatingcomposition was performed. The results are shown in the following Table4.

Example 31

According to the same manner as that of Example 27 except that 50 partsby weight of the particles of Example 6 was used, a coated article wasprepared. And, the specular reflectance of a surface of the resultingcoated article was measured.

In addition, assessment of dispersibility of the prepared coatingcomposition was performed. The results are shown in the following Table4.

TABLE 4 specular assessment of reflectance (%) dispersibility EX.2519.88 ◯ EX.26 27.54 ◯ EX.27 15.23 ◯ EX.28 20.17 ◯ EX.29 19.38 ◯ EX.3018.42 ◯ EX.31 20.53 ◯ COM. EX.18 36.43 X COM. EX.19 35.92 X COM. EX.2078.98 — COM. EX.21 29.96 X

As apparent from Table 4, it is recognized that the coating compositionof this invention has better re-dispersibility, that is, dispersibilitystability also in an aqueous system.

Examples and Comparative Examples of Molded Article Example 32

30 g of the polymer particles coated with silica obtained in Example 12was added to 300 g of a methyl methacrylate resin (MG-5 manufactured bySumitomo Chemical Co., Ltd., refractive index 1.49), the materials wereblended with a food mixer for 3 minutes, supplied to an injectionmolding machine, and injection-molded to obtain a light diffusiblemolded article having a length of 100 mm, a width of 50 mm and athickness of 2 mm.

The total light transmittance, the haze and the diffused lighttransmittance of this light diffusible molded article were measured bythe aforementioned methods, respectively. The results are shown in thefollowing Table 5.

Example 33

According to the same manner as that of Example 32 except that an amountof the polymer particles coated with silica to be added was 45 g per 300g of a methyl methacrylate resin, a light diffusible molded article wasobtained. Further, as in Example 32, the total light transmittance, thehaze and the diffused light transmittance were measured. The results areshown in the following Table 5.

Example 34

According to the same manner as that of Example 32 except that 3 g ofthe polymer particles coated with silica obtained in Example 14 was usedper 300 g of a methyl methacrylate resin, a light diffusible moldedarticle was obtained. Further, as in Example 32, the total lighttransmittance, the haze and the diffused light transmittance weremeasured. The results are shown in the following Table 5.

Example 35

According to the same manner as that of Example 32 except that 30 g ofthe polymer particles coated with silica of Example 15 as a polymerparticle coated with silica was used per 300 g of a methyl methacrylateresin, a light diffusible molded article was obtained. Further, as inExample 32, the total light transmittance, the haze and the diffusedlight transmittance were measured. The results are shown in thefollowing Table 5.

Comparative Example 22

According to the same manner as that of Example 32 except that 3 g ofthe polymer particles obtained in Comparative Example 8 was used per 300g of a methyl methacrylate resin in place of the polymer particlescoated with silica, a molded article was obtained. Further, as inExample 32, the total light transmittance, the haze and the diffusedlight transmittance were measured. The results are shown in thefollowing Table 5.

Comparative Example 23

According to the same manner as that of Example 32 except that 30 g ofthe polymer particles obtained in Comparative Example 9 was used per 300g of a methyl methacrylate resin in place of the polymer particlescoated with silica, a molded article was obtained. Further, as inExample 32, the total light transmittance, the haze and the diffusedlight transmittance were measured. The results are shown in thefollowing Table 5.

Comparative Example 24

According to the same manner as that of Example 32 except that 45 g ofthe polymer particles coated with silica obtained in Comparative Example5 was used per 300 g of a methyl methacrylate resin as a polymerparticles coated with silica, a molded article was obtained. Further, asin Example 32, the total light transmittance, the haze and the diffusedlight transmittance were measured. The results are shown in thefollowing Table 5.

Comparative Example 25

According to the same manner as that of Example 32 except that polymerparticles coated with silica were not blended, and only a methylmethacrylate resin was used, a molded particle was obtained. Further, asin Example 32, the total light transmittance, the haze and the diffusedlight transmittance were measured. The results are shown in thefollowing Table 5.

Example 36

According to the same manner as that of Example 32 except that thecomposite particles obtained in Example 15 were used, a light diffusiblemolded article was obtained. Further, as in Example 32, the total lighttransmittance, the haze and the diffused light transmittance weremeasured. The results are shown in the following Table 5.

Example 37

According to the same manner as that of Example 32 except that thepolymer particles coated with silica obtained in Example 16 were used, alight diffusible molded article was obtained. Further, as in Example 32,the total light transmittance, the haze and the diffused lighttransmittance were measured. The results are shown in the followingTable 5.

Example 38

According to the same manner as that of Example 32 except that 45 g ofthe polymer particles coated with silica obtained in Example 17 wasused, a light diffusing molded particle was obtained. Further, as inExample 32, the total light transmittance, the haze and the diffusedlight transmittance were measured. The results are shown in thefollowing Table 5.

Example 39

3 g of the polymer particles coated with silica obtained in Example 5was added to 300 g of a methyl methacrylate resin (MG-5 manufactured bySumitomo Chemical Co., Ltd., refractive index 1.49), the materials wereblended with a food mixer for 3 minutes, supplied to an injectionmolding machine, and injection-molded to obtain a light diffusiblemolded article having a length of 100 mm, a width of 50 mm and athickness of 2 mm.

The total light transmittance, the haze and the diffused lighttransmittance of this light diffusible molded article were measured bythe aforementioned methods, respectively. The results are shown in thefollowing Table 5.

TABLE 5 total light haze diffused light transmittance(%) (%)transmittance(%) EX.32 83.17 97.55 81.13 EX.33 81.79 98.77 80.78 EX.3489.25 90.21 80.51 EX.35 82.95 98.23 81.48 EX.36 83.52 97.39 81.34 EX.3781.21 98.56 80.04 EX.38 84.23 95.48 80.42 EX.39 88.93 91.83 81.66 COM.EX.22 81.56 87.78 71.59 COM. EX.23 76.32 94.38 72.03 COM. EX.24 76.2196.59 73.61 COM. EX.25 92.34  0.83  0.77

As apparent from Table 5, since the light diffusible molded article ofthis invention retains the higher total light transmittance and thehigher haze as compared with the molded article in which the.conventional polymer particle or composite particle was blended, thediffused light transmittance is as high as 80% or more, and it isrecognized that the diffused light is effectively transmitted.

The polymer particle coated with silica of this invention is excellentin light diffusibility and reflectivity, and can be utilized in manyutilities such as paints, by utilizing those properties. Further, sincethe polymer particle coated with silica of this invention is excellentin light diffusibility and reflectivity and, further, the method forproducing the polymer particle coated with silica of this invention canproduce the particle without applying a strong mechanical shear force,the polymer particle having low Tg can be easily coated with a silicafilm.

In addition, since the coated article of this invention has thesuppressed surface specular reflectance, it is effective in the fieldrequiring matting and glare protection. In particular, since the opticalmember of this invention can be excellent in the light transmittance andthe light diffusibility, it is effective in the field requiring the highlight diffusibility and light transmittability, such as an illuminationequipment cover, a light guide plate, and a screen for a projectiontelevision.

Further, the light diffusible molded article containing the polymerparticle coated with silica of this invention can be used opticalcomponents such as illumination equipment cover, lens, electroconductiveplate, video disc, and screen for projection television, cosmeticcontainer, front plate of vendor machine, signboard, merchandisedisplay, and table container.

1. A spherical or approximately spherical particle comprising: a polymerparticle derived from a polymerizable vinyl-based monomer; and a silicafilm covering the polymer particle, which makes a surface of the polymerparticle exposed so that an aperture ratio of 0.1 to 1 is possessed anda height h of the silica film and a diameter D of the polymer particlecoated with silica have a relationship of 0.5≦h/D<1, wherein the silicafilm includes a polyalkoxysiloxane oligomer condensate.
 2. A coatingcomposition comprising: a polymer particle coated with silica comprisinga polymer particle derived from a polymerizable vinyl-based monomer, anda silica film covering the polymer particle, which makes a surface ofthe polymer particle exposed so that an aperture ratio of 0.1 to 1 ispossessed and a height h of the silica film and a diameter D of thepolymer particle coated with silica have a relationship of 0.5≦h/D<1,the silica film including a polyalkoxysiloxane oligomer condensate; anda binder solution, wherein the binder solution contains a binder resinand a solvent.
 3. The coating composition according to claim 2, whereinan amount of the polymer particle coated with silica to be blended is 1to 150 parts by weight per 100 parts by weight of the binder resin.
 4. Acoated article, wherein the coating composition according to claim 2 iscoated on a substrate.
 5. An optical member, wherein the coatingcomposition according to claim 2 is coated on a transparent substrate.6. The optical member according to claim 5, wherein an amount of thepolymer particle coated with silica to be blended is 20 to 120 parts byweight per 100 parts by weight of the binder resin.
 7. A liquid crystaldisplay wherein the optical member according to claim 6 is used.
 8. Amethod for producing the polymer particle coated with silica accordingto claim 1, wherein the polyalkoxysiloxane oligomer has a weight-averagemolecular weight of 300 to
 3000. 9. A light diffusible molded articlecomprising a transparent resin and a polymer particle coated withsilica, wherein the polymer particle coated with silica comprises apolymer particle derived from a polymerizable vinyl-based monomer, and asilica film covering the polymer particle, which makes a surface of thepolymer particle exposed so that an aperture ratio of 0.1 to 1 ispossessed and a height h of the silica film and a diameter D of thepolymer particle coated with silica have a relationship of 0.5≦h/D<1,and the silica film includes a polyalkoxysiloxane oligomer condensate.10. The light diffusible molded article according to claim 9, whereinthe polymer particle coated with silica has a difference in a refractiveindex from that of the transparent resin of 0.01 to 0.10, and thediffused light transmittance represented by an (equation), diffusedlight transmittance (%)=total light transmittance (%)×haze (%)×0.01, hasa value of 80% or more.
 11. The light diffusible molded articleaccording to claim 9, wherein an amount of the polymer particle coatedwith silica to be blended is 0.1 to 20 parts by weight per 100 parts byweight of the transparent resin.
 12. A method for producing a polymerparticle coated with a silica film which makes a surface of the polymerparticle exposed so that an aperture ratio of 0.1 to 1 is possessed, anda height h of the silica film and a diameter D of the polymer particlecoated with silica have a relationship of 0.5≦h/D<1, the methodcomprising, in the following order, the steps of: uniformly mixing 100parts by weight of a polymerizable vinyl-based monomer, 10 to 500 partsby weight of a polyalkoxysiloxane oligomer which is inert to thepolymerizable vinyl-based monomer, and 0.01 to 10 parts by weight of apolymerization initiator to obtain a monomer composition; aqueoussuspension-polymerizing the polymerizable vinyl-based monomer in themonomer composition in the presence of a suspension stabilizer to obtaina polymer particle; and adding an acid or base catalyst to condense thepolyalkoxysiloxane oligomer.